AsyncSSH创建SFTP客户端错误-太多的值需要解包

Question

我在Sanic应用程序中使用异步SFTP库(运行Asyncio事件循环)来创建SFTP客户端连接。在我的代码中，我是这样做的：

class MyClass:
    async def connect(self, host, username, password, port):
        return await asyncssh.connect(host=host, port=port, username=username, password=password, known_hosts=None)

    async def establish_sftp_client(self, conn):
        return await conn.start_sftp_client()

    # This is my invoker:
    async def create_connection(self, <some args>):
        conn = await self.connect()
        sftp_client = await self.establish_sftp_client(conn)
        ...
        return conn, sftp_client

当我尝试这样做时，我会得到这个错误：

Traceback (most recent call last):
File "/tmp/pycharm_projects/<MY SANIC APP>/requests/helpers.py", line 378, in establish_sftp_client
    return await conn.start_sftp_client()
  File "<MY SANIC APP>/venv/lib/python3.6/site-packages/asyncssh/misc.py", line 182, in __await__
    return (yield from self._coro)
  File "<MY SANIC APP>/venv/lib/python3.6/site-packages/asyncssh/connection.py", line 3503, in start_sftp_client
    encoding=None)
ValueError: too many values to unpack (expected 3)

当我调试它并注销start_sftp_client()实际返回的内容时，我得到如下信息：

(asyncssh.stream.SSHWriter对象位于0x7f51bbb29dd8，asyncssh.stream.SSHReader对象位于0x7f51bbb29da0，asyncssh.stream.SSHReader对象位于0x7f51b99b7978，asyncssh.stream.SSHClientStreamSession对象位于0x7f51bbb29f98) )

因此，当我查看asyncSSH的源代码时，它实际上是返回4 asyncSSH，在start_sftp_client()实际上所做的工作中，它只需要寻找三个：

writer, reader, _ = yield from self.open_session(subsystem='sftp', encoding=None)

，所以这个错误就是thrown...but，为什么？

当我从python控制台运行这个方法时--它工作得很好。从此脚本正确地创建了SFTP客户端：

import asyncssh, asyncio

async def x():
    conn = await asyncssh.connect(host='<host'>, username='some name', password='some pass', port=22, known_hosts=None)
    sftp = await conn.start_sftp_client()
    print("sftp {}".format(sftp)) # This works!

asyncio.get_event_loop().run_until_complete(x())

Answer 1

在将日志语句放置在代码库中之后，最终找到了造成此问题的根本原因。这些行隐藏在一些模糊的文件中：

@asyncio.coroutine
def open_session(self, *args, **kwargs):            
    chan, session = yield from self.create_session(CoreSSHClientStreamSession,
                                                   *args, **kwargs)

    return (asyncssh.stream.SSHWriter(session, chan), asyncssh.stream.SSHReader(session, chan),
            asyncssh.stream.SSHReader(session, chan, asyncssh.constants.EXTENDED_DATA_STDERR))


asyncssh.SSHClientConnection.open_session = open_session

最后一行覆盖异步the中的open_session方法！